Long distance journey: Go faster or ride more efficiently?

[danielrlee]

Does anybody know of a formula to work out the above, based on a fixed distance, battery capacity and charging capability? I know there are other variables involved, but it would be handy to roughly work out the ideal speed for journeys too far on just a single charge.

 

[bowlofsalad]

https://endless-sphere.com/forums/viewtopic.php?f=2&t=73610 Maybe the contents of this thread will help answer your question.

 

[John in CR]

Your charge rate and power consumption at cruise at different speeds is required to do the simple math to figure out which will get you to your destination the quickest. Of course you have to factor in the availabilty of charge points, and if the trip is long enough to require breaks for sleeping, eating, etc. those amounts of time are free charge time, so you could have portions of the journey where riding faster than the average pays off.

 

[Jonathan in Hiram]

In theory it doesn't seem to make a lot of difference, you are limited by charging capacity. Assuming much more than 1kW charging power from a given AC receptacle is asking to trip breakers and make yourself unpopular as well as not getting your charge as you wanted.

If your charge takes a certain fixed time then the faster you go the more of your trip time you spend charging so your average speed increases little if any. Given the logistics of finding a receptacle to plug into and so on I suspect that slower within reason might end up actually getting further per day simply because you spend less of your time trying to find a charging spot.

Aerodynamics is where it's at, get the aero better and speeds go up while range increases.

Work out about half a dozen examples on the Grin simulator and plug in your charging time @ whatever power level you choose, then you can calculate average speed over the entire travel/charge cycle. I tried it and was fairly surprised at how little the average speed changed with riding speed for a given charging rate.

 

[danielrlee]

Cheers for your input guys. I guess what I am looking for is someone that has already done the legwork for me. Maybe a calculator even. Lazy, I know :?

I think that maybe the logistics are more relevant than I'd considered in regards to planning for and locating charge points. Also, some differences come to mind between both our sides of the pond when it comes to panning for a long distance ebike journey. In the UK, 240v AC gives us around 3000w of charging power without worrying about tripping breakers. Also, I think towns are located closer to each other over here, whereas in some parts of the US, travelling 50 miles between charging opportunities isn't uncommon. It does seem that once in a built-up area though, a publicly accessible AC point is quite easy to locate for you guys, whereas in the UK they can be as rare as rocking horse shit.

 

[amberwolf]

I can only say that the faster you go, after some point (typically around 15MPH+) the less efficient it might be, because you lose more to wind resistance.

 

[LockH]

Aerodynamics is where it's at, get the aero better and speeds go up while range increases.

Watt he said... "Aerodynamics" aka "wind resistance" comes up over and over. The way to "ride more efficiently" is to NOT "go faster". ANY "excess" weight also "bad". See kinetic energy re accelerating, going up hills etc where gravity involved.

The one scenario I can think of where faster speeds DO shorten times from A to B, etc is on the water, where a multihulled vessel can lift one or more hulls out of the water using wind pressure or hydrofoils.

 

[Chalo]

Does anybody know of a formula to work out the above, based on a fixed distance, battery capacity and charging capability? I know there are other variables involved, but it would be handy to roughly work out the ideal speed for journeys too far on just a single charge.

You'll use fewer Wh/mile the slower you go, assuming you aren't crawling up hills at grossly inefficient motor speeds. At some point, you run out of time in the day, or opportunities to charge while stationary.

Go slow enough, and you can do it on photovoltaics alone. Might be boring.

 

[danielrlee]

Bear in mind that my question wasn't "how do I ride more efficiently". My thought was that given a high enough charging capability, there must be a point where it'd be quicker to just go faster to capitalise on it.

I guess it's probably only relevant to those running lipo packs who can take advantage of 1-4C charge rates without substantially screwing them up, but it is a question that interests me nonetheless.

 

[KINNINVIEKID]

I ride as fast as I can on long rides as I only have free time during the day and have to be back home by 5pm.
I find that I can get around 110 miles out of my batteries riding like this whereas if I keep to a maximum of 15Mph (on road) I can get 150 miles range.
I am running 48Ah of Multistars on a BBS02 weighing around 125Kg fully loaded.
When I have been using just 16Ah I have needed charging a couple of times and just called into a pub(UK) and they have always been happy to lend me a socket in exchange for a couple of large brandies.

 

[dogman dan]

The maximum efficiency, or distance capability would be ride slow, charge fast. Don't finish a charge, because the last few wh take forever when the charger is only pushing 20 watts vs 250.

You can dope out the answer to your question yourself if you know two things. Watt hours per hour of your charger, and watt hours per mile of the bike at various speeds. And of course, ride time at different speeds.

Then you can make a spread sheet using various combinations. Assuming your charge is constant, for example, 5 amps of 48, then the only variables are the bike wh/mi, and the ride time at different speeds.

So lets say, 56v x 5 amps for your charger. That's 280 watss, or 280 wh per hour. But it's not going to push all that the entire charge, so lets work with the number 250 watt hours per hour.

Now, lets use 48v 10 ah for the battery size. That's about 500 watt hours, so a two hour full charge. But again, it's not going to put that last ah in very fast at all, so lets just use the number two hours, to charge the battery to 9 amp hours full.

Follow all that? Real world numbers you can grab yourself with a watt meter. I'm just estimating for discussion purposes.

So from empty to 9 ah, I'm postulating about 450 watt hours, and it takes two hours to grab that.

Now to the bike. lets use more theoretical numbers, assuming NO pedaling. 15 mph will get you about 20 watt hours per mile. 25 miles per hour will take about 35 watt hours per mile.

Now lets calculate for a slow ride that makes it on one charge, and a faster one that takes two.

450 watt hours / 20 wh per mile is a 22.5 mile ride. It will take 1 hour 30 min.

At 25 mph, it will take 797 watt hours. and take about 50 min total ride time. So you will need to charge enough to get 397 watt hours. At 250 wh per hour, 1.6 hours to charge. Call it 2.5 hours to do the 22.5 mile trip, more or less.

Nearly an hour quicker, to just ride slow in this case. I'd solve the problem with a bigger battery first, rather than a bigger charger. Then once you have the bigger battery, a faster charger will be swell of course.

Now you can see how to figure out your own calculations for your charger and battery.

 

[John in CR]

Bear in mind that my question wasn't "how do I ride more efficiently". My thought was that given a high enough charging capability, there must be a point where it'd be quicker to just go faster to capitalise on it.

I guess it's probably only relevant to those running lipo packs who can take advantage of 1-4C charge rates without substantially screwing them up, but it is a question that interests me nonetheless.

You have to know your actual consumption vs speed to determine the optimum speed. That's because aerodynamics can vary quite a bit between ebikes, and the energy you give back to the wind increases geometrically with speed. The calculator here http://www.kreuzotter.de/english/espeed.htm can give you a reasonable estimate in that regard.

While the theoretical optimum is an interesting mental exercise, the practicalities will dominate in actually doing it. There are certainties for both though. You want to maximize aerodynamics and charging power. The optimum discharge power will always less than charging power, since spending more time charging than riding can never be the optimum. You'll also want to maximize the battery pack size to start the trip or each day with the most energy aboard, but once pack size begins to hurt aerodynamics the math will kick in.

 

[dogman dan]

I only wanted to give you, and the many others who read it, an idea how to calculate times for ride, and charge.

For sure, big battery and not need to charge till home always wins. But some situations that won't work at all because the ride is just too long. That's been my problem with touring, I only had 500watts between two chargers. So every stop I had to make to charge just took intolerably long, charging an already huge pack. Theoretically a 4 hour charge, but in practice more like 5 and a half hours to get totally full. Old batteries charge sloooow.

Grindz, Troy Rank, did much better on his tour. I forget how fast he could charge, but it was more like a 2 hour stop for him to grab a full load. Then he could ride faster and cover more miles than I ever could. He had towns more often where he was riding, so he could stop about every 40 miles, grab an hour or two of charge, and press on at 30 mph or so. That's not a bad cycle, more or less on the bike 2 hours, off the bike 2 hours, repeated 3 times or so. Still a lot of charging time, but getting double my usual daily distance.

For me, the next plug could be 60- 80 miles, and I'd have to ride slow just to make it there at all. Further out west, some big gaps between towns on most of the roads. So my rides could not go any faster with the battery I had, about 1500 wh actual usable capacity.

Bottom line, you want fast charging if you have to sit around at some coke machines outlet at the quickie mart. 500w (48v 5 amps x 2) was not near enough. I'd like to try touring with two satiators ( Still only 700w for two) for chargers, and a bigger battery to go 80 miles at no less than 20 mph. Still a long charge, but the satiator would make a great charger to mount right on the bike.

 

[DrkAngel]

Consider:
distance,
battery size,
range at differing speeds,
pedal contribution
time to recharge (fully or quick)
Faster = overnight charge - Discharge - Charge - Discharge might provide less daily distance than ...
Slower = overnight Charge - Discharge - overnight Charge

Best?
Moderate speed with quick perk up charges at brunch, lunch, mid afternoon snack etc. - (quick charge compatible batteries recommended)
Or just Lunch?
Partial charges supply much better Ah than "full" charges! E.G. 20Ah battery 10A charger = 3 - 1 hour partial charges (30Ah) vs 3 hour+ full charge (20Ah) higher charge rates amplify the disparity!
Fuel your bike while you fuel yourself.
Observe for available outlet before purchasing snack!
Always tip the cashier and ask before plugging in ...?
Be aware of energy cost! - "Mind if I steal 6¢ of electricity to perk up my battery?"

"Generic Mountain bike - motor only.
48V 10ah Lithium battery = 480wh

Anyway
10mph = 46 miles range - 10.4wh/mile
15mph = 30 miles range - 16wh/mile
20mph = 20 miles range - 24wh/mile
25mph = 13 miles rang - 37wh/mile
30mph = 8 miles range - 60wh/mile

See - Speed vs Range

If you travel the same long route on a regular basis ... make a friend along the way.
Stop in for a quicky ... recharge.
eBike forums, clubs or registry?
Help set up a recharge network.

Metricilated 'er up fer ya ...
Generic Mountain bike - motor only.
48V 10ah Lithium battery = 480wh
10mph = 46 miles range ........ 16kph = 74 Kilometer range - 6.5wh/km
15mph = 30 miles range ........ 24kph = 48 Kilometer range - 10wh/km
20mph = 20 miles range ........ 32kph = 32 Kilometer range - 15wh/km
25mph = 13 miles range ........ 40kph = 21 Kilometer range - 23wh/km
30mph = 8 miles range ........ 48kph = <13 Kilometer range - 37wh/km

Remember ...
It's not just, how far you go ...
It's also, how go you far!

 

[dogman dan]

That distance chart comes very close to what I have gotten, with light pedaling. Because of the effect of weather on my range.

As you can imagine, a 5 mph head wind turns a 15 mph ride into the range of a 20 mph ride. Yet you hardly notice 5 mph wind. 20mph effective wind drag, now your range is 33% less than 15 mph!

Stuff like this matters huge when you have a 60-80 mile gap between available plugs. I left for home at 2 am one trip, because with a 20 mph headwind forecast for going home, I was never going to make it later in the day.